Motor control center subunit having moveable line contacts and method of manufacutre

ABSTRACT

A system and method for connecting supply power to motor control components includes use of a motor control center subunit with moveable supply power contacts. After a motor control center subunit is secured into a motor control center compartment, the supply power contacts may be advanced to engage supply power buses. For disconnection, the supply power contacts may be retracted and isolated from the buses before physical removal of the subunit.

CROSS-REFERENCE TO RELATED APPLICATION

The present invention claims the benefit of U.S. provisional applicationSer. No. 60/833,380, filed Jul. 26, 2006.

BACKGROUND OF THE INVENTION

The present invention relates generally to a system and method for motorcontrol, and more particularly, to a subunit for a motor control centerwhich connects motor control components to supply power, and a method ofmanufacture thereof. The system and method described herein provide forconnection of the supply power to the motor control components afterfull installation of the motor control center subunit into the motorcontrol center.

A motor control center is a multi-compartment steel enclosure with a bussystem to distribute electrical power, on a common bus system, to aplurality of individual motor control units mountable within thecompartments. The individual motor control units are commonly referredto as “buckets” and are typically constructed to be removable, pull-outunits that have or are installed behind individual sealed doors on themotor control center enclosure. These buckets may contain various motorcontrol and motor protection components such as motor controllers,starters, contactor assemblies, overload relays, circuit breakers, motorcircuit protectors, various disconnects, and similar devices foroperating high voltage motors. The buckets connect to the supply powerlines of the motor control center and conduct supply power to the lineside of the motor control devices, for operation of motors. Motorcontrol centers are most often used in factories and industrialfacilities which utilize high power electrical motors, pumps, and otherloads.

Typically, when installing or removing motor control center buckets, thepower supply lines are connected or interrupted. To remove such abucket, a deadfront door of the bucket or of the motor control center isopened and an operator manually pulls on the bucket to separate theprimary disconnects, or “stabs,” from the bus system, therebydisconnecting power supply. Installation of a bucket is accomplished ina similar manner, wherein the operator manually pushes the bucket into acompartment of the motor control center to engage the bucket stabs withthe bus system, and thus connect the system to supply power. The lineconnections or stabs may be difficult to maneuver manually when anoperator is supporting the entire bucket or when the stabs are notvisible.

Attempts have been made to improve upon the manual installation anddisconnection of motor control center buckets and supply powerconnections from live supply power lines, risers, and/or a vertical busof a motor control center. Other systems have employed pivotable handlesinside the buckets to pivot line connectors to and from supply lines.However, many of these systems require that the bucket or compartmentdoor be open to manipulate the handles and line stabs.

It would therefore be desirable to design a motor control center bucketassembly that overcomes the aforementioned drawbacks. Thus, it would bedesirable to provide for remote connection or disconnection of the linestabs of a bucket to the power supply lines or bus of a motor controlcenter from a distance. In the event of an arc or arc flash, any heatedgas, flame, and/or the arc itself should preferably be contained behindthe bucket compartment door or “deadfront.”

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides a system and method for installing amotor control center subunit or bucket into a motor control center andelectrically connecting motor control components of the bucket to apower supply. The system and method utilize moveable line stabs toengage the power supply (such as a series of bus bars) after the buckethas been secured in the motor control center, in order to containpotential arc flashes.

Therefore, in accordance with one aspect of the present invention, acontrol module for a motor control center is provided. The controlmodule includes a housing having a plurality of conductive contactstherein. The housing has a front panel and is designed to seat in amotor control center whereupon the front panel forms a front face of themotor control center. The control module also includes an engagementmechanism which is attached to the housing and is in operableassociation with the plurality of conductive contacts. The engagementmechanism moves the plurality of conductive contacts between a retractedposition and an extended position while the control module housing isseated in the motor control center and the front panel is in a closedposition.

In accordance with another aspect of the invention, a method ofmanufacturing a control module for a motor control center is provided.The method includes assembling a control module housing to have at leasta front panel and to seat in a motor control center, disposing amoveable guide within the control module housing to guide motion of atleast one supply contact from a first position to a second position,attaching the at least one supply contact to the moveable guide, andproviding for advancement of the at least one supply contact and themoveable guide when the front panel of the control module housing issecured against the motor control center compartment.

According to a further aspect of the invention, a motor control centersubunit includes a subunit housing, an actuating mechanism, and anisolator assembly. The subunit housing is designed to be installed in amotor control center. The actuating mechanism is disposed within thesubunit housing and is constructed to move a plurality of lineconnectors between a retracted position and an extended position. Theisolator assembly is configured to electrically shield the plurality ofline connectors prior to engagement of the plurality of line connectorswith a line power.

In accordance with another aspect of the invention, a motor controlcenter is provided that includes a frame and at least one control unit.The frame encloses a supply power bus and has at least one compartment.The at least one control unit is configured for substantially sealedinstallation in the at least one compartment, and includes at least onesupply power contact, a drive configured to move the at least one supplypower contact for engagement and disengagement with the supply powerbus, and a drive actuator designed to actuate the drive from without thecontrol unit when the control unit is installed in the at least onecompartment.

Various other features and advantages of the present invention will bemade apparent from the following detailed description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate one preferred embodiment presently contemplatedfor carrying out the invention.

In the drawings:

FIG. 1 is a partial perspective view of a motor control center subunitinstalled in a motor control center.

FIG. 2 is a perspective view of the motor control center subunit of FIG.1, removed from the motor control center.

FIG. 3 is a top view of the motor control center subunit of FIG. 1showing a number of stabs in a retracted position.

FIG. 4 is top view of the motor control center subunit of FIG. 3 showingthe stabs in a test position.

FIG. 5 is a top view of the motor control center subunit of FIG. 4showing the stabs in an extended position.

FIG. 6 is a cross-sectional view of the motor control center subunit ofFIG. 3 taken along line 6-6 of FIG. 3.

FIG. 7 is a detailed view of a portion of the motor control centersubunit of FIG. 6 showing an arc shield, line contact, and supplyconductor thereof.

FIG. 8 is a detailed view of the motor control center subunit of FIG. 7showing line contact extension.

FIG. 9 is a plan view of a control handle of one embodiment of thepresent invention.

FIG. 10 is a side view of the control handle of FIG. 9.

FIG. 11 is a plan view showing the control handle of FIG. 9 rotatedninety degrees.

FIG. 12 is a side view of the control handle of FIG. 11.

FIG. 13 is a side view showing the control handle of FIG. 11 depressedinto a motor control center subunit.

FIG. 14 is a plan view showing the control handle of FIG. 11 rotatedninety degrees.

FIG. 15 is side view of the control handle of FIG. 14.

FIG. 16 is a partial perspective view of the motor control centersubunit of FIG. 1 showing an alternate embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description makes reference to supply power, supply powerlines, motor power, load power, line power, and the like. It isappreciated that such terms may refer to a variety of both common anduniquely conditioned voltage and current characteristics, including butnot limited to, three phase AC power, single phase AC power, DC power,multiple DC power lines, or any combination thereof. Such powercharacteristics will be generally referred to as being provided on abus, supply line, or riser of a motor control center. However, it isappreciated that the present invention may find applicability in otherpower connectivity configurations, adapted or apart from motor controlcenters. An example of supply power commonly used in motor controlcenters is 480V three-phase AC power distributed over three separatesupply buses.

Referring to FIG. 1, a partial perspective view of a motor controlcenter structure 10 is shown. As discussed above, motor control centersmay include compartments or enclosures for multiple control modules orbuckets 11, 13, 14, 15, 16, 17. Bucket 16 is shown fully installed intomotor control center compartment or enclosure 12 such that its frontpanel 18 is seated securely against the periphery of enclosure 12 andflush with the front panel 20 of bucket 14. In this regard, bucket 16includes a number of latching mechanisms 22 on front panel 18 so that anoperator may lock bucket 16 into place once installed. In someembodiments, front panel 18 may be a door having a set of hinges 19 inorder to permit access to components within bucket 16 while bucket 16 isinstalled in enclosure 12 of motor control center 10. However, even whenclosed or sealed, front panel or door 18 still permits access to circuitbreaker assembly 28, optional indicators 24, 26, and line contactactuator 31. Line contact actuator 31 is a mechanism for engaging linecontacts (FIG. 2) with line power from the motor control center 10.Thus, even when bucket 16 is fully installed in enclosure 12 and latches22 have been secured, an operator may still use circuit breaker handle30 and may open slide 32 to insert crank 34 to move one or more stabs(not shown) of the bucket 16.

Referring now to FIG. 2, a perspective view of a motor control centerbucket 16 is shown. It is noted that bucket 16 may have a housing thatincludes a number of panels surrounding bucket 16 to fully or partiallyenclose the components thereof. As shown, bucket 16 includes a pair ofside panels 52 and a front panel 18, which support motor control devicesand internal bucket components. An upper panel and a rear panel havebeen removed to show the internal components of bucket 16. Front panel18 is configured to fit snugly and securely within a motor controlcenter such that a rim 38 of the front panel 18 seats against the innerperiphery (not shown) of a motor control center enclosure. For purposesof dust protection, rim 38 may optionally include a compressible orflexible seal, such as a rubber seal, or other gasket-type component.Once bucket 16 is inserted into a motor control center enclosure, latchmechanisms 22 may be turned with a key, a screwdriver, or by hand sothat latch arms 40 abut an inner surface of the outer periphery (notshown) of an enclosure to hold bucket 16 in place and/or prevent bucket16 from being removed. Similarly, an automatic latch 60 is shown in anengaged position. Upon advancement of line contacts or stabs 46, 48, 50automatic latch 60 is triggered to engage a frame or lip of the motorcontrol center unit in which bucket 16 is installed.

When slide 32 of line contact actuator 31 is moved aside, an opening 36is exposed. Opening 36 preferably has a unique configuration to accept aspecialized crank 34 (as shown in FIG. 1). In other embodiments, to bedescribed below, a manually drivable handle may extend through opening36 or a remotely operable motor may be the actuator 31. When slide 32 ismoved aside as shown, slide 32 extends over a portion of front panel 18.Thus, in embodiments in which front panel 18 is a hinged door, movingslide 32 to expose opening 36 will inhibit a user from opening frontpanel 18.

Bucket 16 also includes a number of conductive line contacts or stabs44, 46, 48, 50. Control power contact 44 is preferably fixedly attachedto the rear of bucket 16, whereas supply power stabs 46, 48, 50 aremoveable with respect to bucket 16. However, it is appreciated thatcontrol power contact 44 may also be moveable in a similar manner toline power stabs 46, 48, 50. Control power contact 44 is of a suitableconstruction to conduct a control power (typically a few volts) to motorcontrol components (not shown) disposed within bucket 16. In embodimentswhere control power contact 44 is permanently positioned at the rear ofbucket 16, control power contact 44 will engage a control power supplyline or bus upon installation of bucket 16 into a motor control center.

Supply power stabs 46, 48, 50, on the other hand, do not engage supplypower lines or buses when bucket 16 is installed into a motor controlcenter. Rather, stabs 46, 48, 50 are initially in retracted position 42,as shown in FIG. 2, disposed inside bucket 16. One of skill in the artwill appreciate that a number of configurations of supply power stabs46, 48, 50 may be utilized. In the embodiment shown, stabs 46, 48, 50are shaped to grasp about a supply line, bus, or riser of the motorcontrol center 10 of FIG. 1. A line contact or stab assembly 58 includesa stab bracket 59 to which the stabs 46, 48, 50 are attached. Stabbracket 59 holds stabs 46, 48, 50 in an orientation for subsequentengagement with the supply power lines or buses of motor control center10 of FIG. 1. It is recognized, however, that stab assembly 58 of FIG. 2may include any number of configurations, such as for independentlymoveable stabs, for other than three stabs, or for actuation by otherthan a shaft, as will be described below. A shutter or isolator assembly54 is disposed in the rear of bucket 16, between stab assembly 58 andthe exterior of bucket 16. Isolator assembly 54 includes a number ofmoveable shutters 56 which operate to either expose or isolate the stabs46, 48, 50 from the power lines or buses of the motor control center 10of FIG. 1.

FIG. 3 depicts a top view of bucket 16, with all housing panels removedexcept for front panel or door 18. As shown, stab assembly 58 haspositioned stabs 46, 48, 50 in a retracted position 42 wherein the stabs46, 48, 50 are located inside bucket 16. Accordingly, shutters 56 ofshutter assembly 54 are closed, isolating the stabs 46, 48, 50 from thesupply power bus or line of a motor control center such as shown inFIG. 1. As shown in FIG. 3, each shutter 56 includes two separateshielding members 62 and 64, 66 and 68, 70 and 72. The shutter 56 forstab 46 includes a left shielding portion 62 and a right shieldingportion 64, each being angled toward stab 46. Likewise the shutters 56for stabs 48 and 50 include left shielding portions 66, 70 and rightshielding portions 68, 72 respectively, each being angled toward thecorresponding stab. However, the shutter 56 for stab 50 includes anadditional mechanical connection 74. That is, a shutter arm 74 isprovided to control a shutter indicating mechanism 76 which displays toan operator via front panel indicator 26 whether the shutters 56 areopen or closed, as will be described in further detail below. Similarly,a cam or bell crank 80 is attached via rod 78 to stab assembly 58 totranslate movement of the stab to a microswitch 82. Microswitch 82operates to turn on and off the supply of control power from controlpower contact 44 to motor control components, such as contactors oroverload relays (not shown), of bucket 16.

Referring now to FIG. 4, the bucket 16 is shown having the stab assembly58 in a test position 43. Stabs 46, 48, and 50 have been advanced to apoint or test position 43 at which they nearly touch or just touchshutters 56, but shutters 56 are still closed. Since shutters 56 areclosed, stabs 46, 48, 50 are isolated from supply power buses, thuspreventing arcs from occurring between stabs 46, 48, 50 and the buses.Being in the test position, stab bracket 59 is moved forward such thatactuating shaft or drive 84 is visible. Preferably, shaft 84 is a rotarydrive shaft and is connected to the socket of opening 36 shown in FIG. 2for operation via crank 34, shown in FIG. 1. Referring back to FIG. 4,during the advancement of stab assembly 58, automatic latch 60 has beentriggered to engage the enclosure of the motor control center into whichbucket 16 has been installed. Also due to the advancement of stabassembly 58, rod 78 is pulled by stab bracket 59 such that cam 80 hasrotated away from microswitch 82. Microswitch 82 is thus actuated topermit control voltage from the control power contact 44 to a motorcontrol component, such as a contactor or overload relay (not shown). Itis appreciated, however, that microswitch 82, cam 80 and rod 78 areoptional. In other words, embodiments of the present invention maysimply permit control voltage to pass through control power contact 44directly to motor control components immediately upon installation ofbucket 16 into a motor control center when contact 44 engages a controlpower bus.

FIG. 5 depicts another top view of the bucket 16 wherein the stabs 46,48, 50 are in an extended/engaged position 45. In operation, stabs 46,48, 50 are advanced or extended from the test position 43 of FIG. 4towards shutters 56 and impinge upon angled portions 62-72 of theshutters 56. As the stabs 46, 48, 50 are forced forward into and againstthe surfaces of shutters 56, the stabs 46, 48, 50 separate the leftangled portions 62, 66, 70 and right angled portions 64, 68, 72 of theshutters 56 to expose the stabs 46, 48, 50 to supply power buses 88, 90,92, respectively. Preferably, a biasing or closure force is provided tobias the right angled portions 64, 68 72 and the left angled portions62, 66, 70 towards one another, so that the shutters 56 automaticallyclose upon retraction of stabs 46, 48, 50. It is recognized thatnumerous other ways of opening and closing shutters 56 are possible andcontemplated. For example, rather than employing two shutter portionsfor each shutter, one shutter portion having one beveled surface couldbe slid aside by the advancement of the stabs. Or, the shutters could beconnected for manipulation by the turning of rotary shaft 84. Thus, theshutters 56 could comprise one or several sliding panels with or withoutbeveled surfaces. In other words, shutters 56 may be operated to openand close by the movement of the stabs, by the movement of the stabassembly, by the turning of the actuating shaft, by other actuatingcomponents, or by a manual control. Regardless, once the stabs 46, 48,50 have penetrated through shutters 56, the stabs 46, 48, 50 may beadvanced or extended to engage power supply bus bars 88, 90, 92.

Also shown in FIG. 5 is a second microswitch 94 connected to activateand deactivate circuit breaker 30. When stabs 46, 48, 50 reach the fullyengaged position 45 with bus bars 88, 90, 92, stab bracket 59 of stabassembly 58 actuates microswitch 94. Microswitch 94 permits closure ofcircuit breaker 30, completing the circuit between bus bars 88, 90, 92and the line side of motor control components (not shown) in bucket 16.

Likewise, for removal of bucket 16, circuit breaker 30 is opened,disconnecting supply power to the motor control devices (not shown) ofbucket 16. Stabs 46, 48, 50 may then be retracted from bus bars 88, 90,92 by a reverse motion of rotary shaft 84. Once stabs 46, 48, 50 passshutters 56, the right and left portions 62-72 thereof willautomatically close together to isolate the stabs from bus bars 88, 90,92. Preferably, the shutter portions 62-72 and all or some of thehousing panels, including front panel 18 and a rear panel (not shown),of bucket 16 are plastic or other insulating material. After stabs 46,48, 50 have been fully retracted, automatic latch 60 will release fromengagement with the motor control center, and an operator may then slidebucket 16 out of the motor control center.

Referring now to FIG. 6, a cross-sectional view of bucket 16 taken alongline 6-6 of FIG. 3 is shown. The left angled portion 66 of a shutter 56is shown isolating the central stab 48, since stab 48 is in theretracted position 42 of FIG. 3. In FIG. 6, it can be seen that stabassembly 58 holds stab 48 in position and engages rotary shaft 84, shownin section. Therefore, FIG. 6 illustrates the moving components used toactuate a stab 48. An operator may use a ratchet or crank (not shown)through opening 36 of slide 32 to turn rotary shaft or worm gear 84. Astab guide 96 includes a thread bearing 100 to transform the rotationalmotion of rotary shaft 84 into a translational motion of stab assembly58. Thus, rotary shaft 84 and stab guide 96 may generally be referred toas a racking-type actuating mechanism for extending and retracting thestabs 46, 48, 50, relative to bucket 16. As stab assembly 58 is rackedor otherwise advanced towards the extended or engaged position 45 shownin FIG. 5 (i.e. a motion to the left, as oriented in FIG. 6) stab 48will impinge upon shutters 66. Also, a sloped lip 104 of stab assembly58 will strike a bottom portion 106 of latch 60. As sloped lip 104follows the advancing motion of the stab assembly 58, it will rotatelatch 60 into an upward position wherein bottom portion 106 rests onstab guide 96 and latch 60 extends through a groove 98 of motor controlcenter 10, shown in FIG. 1, to retain bucket 16 therein.

FIG. 7 is an enlarged view of the stab 48 and shutter 66 area of thecross-sectional view of FIG. 6. Conductive stab 48 is coupled to aflexible conductor 130, such as a cable, via a coupling portion 132 ofstab assembly 58. Flexible conductor 130 is of a construction suitableto conduct supply power, via stab 48, to the line side of a motorcontrol component (not shown). As shown in FIG. 8, when stab 48 and stabassembly 58 are racked or otherwise advanced forward to an extendedposition 45, flexible conductor 130 flexes to maintain electricalconnectivity with stab 48 via coupler 132. Accordingly, the motion ofstab 48 relative to bucket 16 does not interfere with the connectivityof the stab 48 with a motor control component.

Referring now to FIGS. 9-15, an alternative stab actuating feature isshown. A manually drivable handle 116 may replace or be used incombination with the crank 34 of FIG. 1 and racking mechanism of FIG. 6.In such embodiments, the rotary shaft or worm gear 84 depicted inprevious embodiments may be replaced with a non-tapped shaft or roddirectly connected to stab assembly 58. FIG. 9 shows such a handle 116in a locked, starting position 118 that corresponds to the stabsdisengaged position 42 of FIG. 3. As shown in FIG. 10, handle 116 isseparated and biased from front panel 18 of a bucket by a spring 120 andextends through stab actuating opening 36. By rotating handle 116 ninetydegrees, as shown in FIGS. 11 and 12, handle 116 may be unlocked 122. Insome embodiments, an interlock system may be included to preventunlocking of handle 116 until bucket 16 is fully installed into a motorcontrol center. Such an interlock may be incorporated into the shaft 84of handle 116. Once unlocked, handle 116 may be driven or depressedtowards front panel 16, compressing spring 120, as shown in FIG. 14. Thedepressed position 124 of handle 116 corresponds to the stabs engagedposition of FIG. 5. Handle 116 may then be rotated another ninetydegrees 126, as shown in FIG. 15, to lock the handle in the stabsengaged position 124, against the force of spring 120. For disengagementof the stabs, handle 116 is rotated to unlocked orientation 122, pulledoutward to the stab disengaged position 42 and turned ninety degrees toa locked position 118. In a general sense, therefore, embodiments of thepresent invention may include various configurations of simplified,manual actuation of the stabs, similar to that shown in FIGS. 9-15.

In other embodiments, it may be desirable to use more automatedactuation of the stabs of a motor control center bucket. Accordingly,FIG. 16 depicts an embodiment of a motor control center bucket 16 inwhich a motor drive 128 is included. Motor drive 128 may replace oraugment a racking mechanism or a manual actuation system, such asdescribed above. Preferably, motor drive 128 is a small DC motor and maybe powered by a battery or by an electrical connection with motorcontrol center 10, such as via the control power contact 44 shown inFIG. 2 or a similar plug or connection. It is recognized, however, thatmany other types, sizes, and configurations of motor drive 128 areequivalently applicable. For example, it may be desirable to connectmotor drive 128 inside bucket 16. Further, it is contemplated that motordrive 128 could be remotely operable, and could be either hardwired orwirelessly connected for operation. It is also contemplated that motordrive 128 may be connected remotely via an elongated shaft or cable tooperate rotary shaft 84 from a distance.

Accordingly, one embodiment of the present invention includes a controlmodule for a motor control center. The control module includes a housinghaving a plurality of conductive contacts therein and a front panel, thecontrol module being designed to seat in a motor control center suchthat the front panel forms a front face of the motor control center. Thecontrol module also includes an engagement mechanism which is attachedto the housing and is in operable association with the plurality ofconductive contacts. The engagement mechanism moves the plurality ofconductive contacts between a retracted position and an extendedposition while the control module housing is seated in the motor controlcenter and the front panel is in a closed position.

Another embodiment of present invention includes a method formanufacturing a control module for a motor control center in which acontrol module housing is assembled to have at least a front panel andto seat in a motor control center, a moveable guide is disposed withinthe control module housing to guide motion of at least one supplycontact from a first position to a second position, and the at least onesupply contact is attached to the moveable guide. The method alsoincludes providing for advancement of the at least one supply contactand the moveable guide when the front panel of the control modulehousing is secured against the motor control center compartment.

In another embodiment of the present invention, a motor control centersubunit includes a subunit housing, an actuating mechanism, and anisolator assembly. The subunit housing is designed to be installed in amotor control center. The actuating mechanism is disposed within thesubunit housing and is constructed to move a plurality of lineconnectors between a retracted position and an extended position. Theisolator assembly is configured to electrically shield the plurality ofline connectors prior to engagement of the plurality of line connectorswith a line power.

In accordance with another embodiment of the present invention, a motorcontrol center is provided. The motor control center includes a frameenclosing a supply power bus and having at least one compartment, and atleast one control unit. The at least one control unit is configured forsubstantially sealed installation in the at least one compartment, andincludes at least one supply power contact, a drive configured to movethe at least one supply power contact for engagement and disengagementwith the supply power bus, and a drive actuator designed to actuate thedrive from without the control unit when the control unit is installedin the at least one compartment.

The present invention has been described in terms of the preferredembodiment, and it is recognized that equivalents, alternatives, andmodifications, aside from those expressly stated, are possible andwithin the scope of the appending claims.

1. A control module for a motor control center comprising: a controlmodule housing having a plurality of conductive contacts therein, thecontrol module housing having a front panel and designed to seat in amotor control center wherein the front panel forms a front face of themotor control center; and an engagement mechanism attached to thehousing and in operable association with the plurality of conductivecontacts to move the plurality of conductive contacts between aretracted position and an extended position while the control modulehousing is seated in the motor control center and the front panel is ina closed position.
 2. The control module of claim 1 further comprisingan isolator assembly configured to alternatingly shield the plurality ofconductive contacts from, and expose the plurality of conductivecontacts to, at least one supply bus.
 3. The control module of claim 2wherein the isolator assembly is further configured to open and close atleast one shutter to alternatingly shield and expose the plurality ofconductive contacts.
 4. The control module of claim 1 wherein the frontpanel of the control module housing substantially seals shut acompartment of the motor control center when in the closed position. 5.The control module of claim 1 wherein the engagement mechanism comprisesat least one of a rotary drive mechanism, a hand-operable mechanism, anda motor drive mechanism.
 6. The control module of claim 1 furthercomprising a conductive contacts assembly configured to position theplurality of conductive contacts for engagement with at least one supplybus when the plurality of conductive contacts is in the extendedposition.
 7. The control module of claim 6 wherein the contact assemblyis further configured to translate a movement of the engagementmechanism into a movement of the plurality of conductive contacts. 8.The control module of claim 1 wherein the front panel is one of hingedor fixedly attached to the control module housing.
 9. A method ofmanufacturing a control module for a motor control center comprising:assembling a control module housing to seat in a motor control centercompartment, the control module housing having at least a front panel;disposing a moveable guide within the control module housing to guidemotion of at least one supply contact from a first position to a secondposition; attaching the at least one supply contact to the moveableguide; and providing for advancement of the at least one supply contactand the moveable guide when the front panel of the control modulehousing is secured against the motor control center compartment.
 10. Themethod of claim 9 wherein disposing a moveable guide within the controlmodule includes arranging the moveable guide to linearly translate theat least one supply contact between the first position and the secondposition.
 11. The method of claim 9 wherein attaching the at least onesupply contact to the moveable guide includes attaching three supplycontacts to the moveable guide for connection to a three phase powersupply.
 12. The method of claim 9 further comprising positioning ashield assembly at an end of the control module housing opposite thefront panel.
 13. The method of claim 12 wherein positioning the shieldassembly includes disposing at least one moveable shutter within theshield assembly to alternatingly isolate and expose the at least onesupply contact.
 14. The method of claim 9 further comprisingconstructing the front panel to permit actuation of the moveable guidetherethrough.
 15. The method of claim 9 wherein assembling the controlmodule housing includes constructing the front panel to securely sealagainst an inner periphery of the motor control center compartment tocontain arc flash.
 16. The method of claim 9 wherein providing foradvancement of the at least one supply contact includes providing atleast one of a rotary drive for crank operation, a handle for manualoperation, and an electric motor for motor-driven operation.
 17. A motorcontrol center subunit comprising: a subunit housing designed to beinstalled in a motor control center; an actuating mechanism disposedwithin the subunit housing and constructed to move a plurality of lineconnectors between a retracted position and an extended position; and anisolator assembly configured to electrically shield the plurality ofline connectors prior to engagement of the plurality of line connectorswith a line power.
 18. The motor control center subunit of claim 17wherein the plurality of line connectors is disposed inside the subunithousing when in the retracted position and extends outside the subunithousing when in the extended position.
 19. The motor control centersubunit of claim 17 further comprising a front panel of the subunithousing designed to substantially seal against a periphery of anenclosure of the motor control center when the subunit housing isinstalled therein.
 20. The motor control center subunit of claim 19further comprising at least one interlock connected to retain thesubunit housing in the enclosure of the motor control center duringengagement of the plurality of line connectors with the line power. 21.The motor control center subunit of claim 19 wherein the subunit housingfurther comprises an opening in the front panel designed to permitoperation of the actuating mechanism when the subunit housing isinstalled in the motor control center.
 22. The motor control centersubunit of claim 17 wherein the actuating mechanism comprises at leastone of a cranking mechanism, a remotely controllable motor, and aninsertable handle.
 23. The motor control center subunit of claim 17further comprising a plurality of flexible conductors electricallyconnected to the plurality of line connectors to conduct power therefromto a line side of control components within the subunit housing.
 24. Themotor control center subunit of claim 17 further comprising a controlpower conductor disposed at an outer surface of the subunit housing andconfigured to engage a control power supply and conduct a control powerto control components within the subunit housing.
 25. The motor controlcenter subunit of claim 17 wherein the plurality of line connectorsincludes three stabs configured to establish electrical communicationwith a set of three-phase bus bars.
 26. The motor control center subunitof claim 17 wherein the isolator assembly further comprises at least onepair of angled shutter surfaces engageable by the plurality of lineconnectors.
 27. The motor control center subunit of claim 17 wherein theactuating assembly is further constructed to advance the plurality ofline connectors to a test position intermediate of the retractedposition and the extended position.
 28. A motor control centercomprising: a frame enclosing a supply power bus, the frame having atleast one compartment; at least one control unit configured forsubstantially sealed installation in the at least one compartment, thecontrol unit comprising: at least one supply power contact; a driveconfigured to move the at least one supply power contact for engagementand disengagement with the supply power bus; and a drive actuatordesigned to actuate the drive from without the control unit when thecontrol unit is installed in the at least one compartment.
 29. The motorcontrol center of claim 28 wherein the at least one control unit furthercomprises a fixed control power contact constructed to engage a controlpower supply and provide control power to a motor control component ofthe control unit.
 30. The motor control center of claim 28 wherein theat least one control unit further comprises a contact guide configuredto translate movement of the drive to linearly move the at least oneline contact for engagement and disengagement with the supply power bus.31. The motor control center of claim 30 wherein the drive and thecontact guide are arranged to move the plurality of contacts a distancesuch that the plurality of contacts are within the control unit whenfully disengaged from the supply power bus and are outside the controlunit when engaged with the supply power bus.
 32. The motor controlcenter of claim 28 wherein the drive of the at least one control unitcomprises a rotary shaft.
 33. The motor control center of claim 28wherein the at least one control unit further comprises an isolatorassembly configured to alternatingly shield and expose the at least oneline contact to the supply power bus.
 34. The motor control center ofclaim 28 wherein the drive actuator of the at least one control unitcomprises at least one of a motor, a handle, and a crank.
 35. The motorcontrol center of claim 28 wherein the at least one control unit furthercomprises a front panel to form a front face of the motor control centerwhen the at least one control unit is installed in the motor controlcenter.
 36. The motor control center of claim 35 wherein the front panelis one of hinged to the at least one control unit to provide access tocomponents therein and fixedly attached to the at least one controlunit.